1. Field of the Invention
The invention pertains to the field of chain or belt tensioners. More particularly, the invention pertains to a chain or belt tensioner with a ratcheting device.
2. Description of Related Art
In chain and belt tensionsers, pistons are urged from their housings by a spring or spring plus hydraulic pressure. Check valves were added to tensioners between the pressurized fluid source and the fluid chamber formed between the housing and the piston to prevent backflow of the hydraulic fluid out of the fluid chamber. The rate of leakage, of the piston to the bore clearance, allows the retraction of the piston as makeup fluid subsides or ceases. When the rate of leakage increases, the restriction on retraction of the piston softens and when the rate of leakage decreases, the restriction on retraction of the piston stiffens. When chain load spikes or a loss of fluid pressure is present, retraction of the plunger occurs and if the retraction of the plunger is excessive, loss of chain control or other undesirable effects occur. Therefore, limiting the amount of piston retraction is desirable.
A ratchet device that is used to limit the piston retraction must allow the plunger to retract and reduce chain load when fluid pressure is reduced during engine shutdown, but not so much as to leave the chain uncontrolled during engine restart. The retraction of the piston is limited by the amount of backlash added to the ratchet.
One example of a tensioner that uses a ratchet device is shown in prior art
Prior art
Another example is U.S. Pat. No. 6,120,402. In one embodiment of U.S. Pat. No. 6,102,402, two wedges define an extending member in a groove. A stepped groove holds the extending members. A side piece of the external rack member has a lower end with an upper surface and a lower surface. The lower end travels axially in a groove of the housing. The lower limit on axial movement of the lower end is the surface of the groove. During operation the limited movement of the lower end of the rack member in the groove of the housing enables limited backward movement of the slide and the piston relative to the housing and thus a small amount of backlash.
In an alternative embodiment, the rack member is formed of multiple pieces. Three pieces are assembled and held together by spring, which forms a cylindrical part. The spring and external rack are held together within the tensioner housing by a pin. The piston slides within the bore and the extending member of the rack slides within the grooves formed on the side of the piston. The extending member includes an upper surface and a lower surface. The lower surface connects with the side pieces by an angled portion. During operation backlash of the piston is limited by the space in the grooves formed between the wedges. As the piston is pushed further outward from the housing, the external member slides over the successive wedge or piston rack portion and is then held within the next groove. A stepped groove is formed so that the rack extending member catches in the stepped groove and stops the piston from leaving the tensioner housing.
A tensioner including a housing having a bore, a hollow piston, a piston spring, a check valve between the source of pressurized fluid and hollow piston, and a pawl plate. The hollow piston is slidably received within the bore of the housing and forms a fluid chamber with the bore. The hollow piston also has a plurality of grooves formed along the outside thereof. The piston spring biases the piston in an outward direction from the bore. The pawl plate has a bottom with a protruding pawl ridge that meshes with the grooves on the piston. The pawl plate is received by the housing and receives a portion of the piston. One side of the pawl plate is biased in the outward direction by a vertical spring or springs and in a lateral direction by a horizontal spring.
The tensioner includes a housing 330, which receives a bore 304. The hollow piston 320 is slidably received by bore 304. The bore 304 within the housing 330 forms a fluid chamber (not shown) with the interior of the hollow piston 320. The fluid chamber receives fluid from a pressurized source (not shown) through fluid line 336 and check valve 302. The check valve 302 allows fluid to enter the fluid chamber only. The outside of the hollow piston 320 has a piston shoulder 316 and a series of piston teeth 310 integrally formed on the piston 320, including a stop ring 308. The piston is biased in an outward, extending direction from the housing by spring 306.
A pawl plate 314 is supported on top of the piston shoulders 316 by vertical pawl springs 312 received by holes 342 in the housing. The pawl plate has flat top and a recessed bottom, which has a protruding ridge or pawl that meshes with the piston rack. The vertical pawl spring 312 biases a portion of the pawl plate 314a in a vertical direction against the bottom of the cover plate 318. Another portion of the pawl plate 314b is biased in a horizontal or lateral direction by pawl spring 326 received between body wall 322 of the housing 330 and a retainer 324. The retainer 324 aids in keeping the piston 320 centered in the bore 304 of the housing 330 and preventing the horizontal pawl spring 326 from cocking. The horizontal pawl spring 326 is kept from exiting the housing 330 of the tensioner by a stop or ball 352. The pawl plate 314b engages the shoulder 316 or the piston rack depending on the position of the piston 320. The piston 320 is allowed to retract into the bore 304 a distance equal to the amount of backlash or clearance 350 between the pawl plate 314b and the edge of the bore housing 354. The pawl plate 314 is covered by a cover plate 318 that receives rivets 348 integrally formed on the housing 330.
A resetting slot 334 is present adjacent to the vertical pawl spring 312 and pawl plate 314a. A key or screwdriver (not shown) may be inserted into the resetting slot 334 to slide the pawl plate 314 against the retainer 324 and the force of the horizontal spring 326 against the housing wall 332, disengaging the pawl plate 314 from the piston shoulder 316 or the piston rack and allow the piston 320 to center and reset as shown in
The vertical pawl springs may be replaced by a conical spring around the piston.
Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.